The invention relates to a vibrating drum for soil tamping machines, whose vibration amplitude can be changed continuously, to the operator""s choice.
It is known that soil tamping machines substantially consist of a pair of vibrating drums supported by a frame, on which there stands a cabin for the driver and propulsion means so as to make the machine self-propelled.
In some embodiments, the frame is divided into two portions, each housing one of the vibrating drums, connected in an articulated way by means of a universal joint which co-operates with the steering wheel.
In order to easily tamp the soils, the drums must have a suitable centrifugal force that is defined by their speed of rotation, and they must also vibrate with an amplitude having a suitable value for the type of soil to be tamped.
In fact, a man skilled in the art knows that for soils consisting of earth or of stabilized materials, an optimum tamping is attained by making the drums vibrate with high vibration amplitudes, whereas low vibration amplitudes are adapted to tamp soils consisting of bituminous materials.
The methods for manufacturing the vibrating drums that equip the tamping machines of the known type present on the market have the rotation shaft of the drum provided with a vibration device, which by changing the frequency of rotation of the shaft itself, changes the centrifugal force of the drum.
On the other hand, the vibration amplitude can have two different values attainable by changing the eccentricity of a mass connected to the rotation shaft of the drum.
More precisely, the vibrating shaft is provided with an eccentric mass which, according to the direction of rotation of the shaft, moves into a recessed or protruding position so as to determine two different amplitude values in vibration.
Thus, the vibrating drums of the known type that are manufactured according to the above methods and that are usually applied to the tamping machines present on the market, exhibit the known limit of not having the possibility of changing with continuity the amplitude of their vibration. Accordingly, they do not attain the optimum tamping of all types of soil. The present invention is intended to overcome said known limits.
In particular, an object of the present invention is that of providing a vibrating drum for soil tamping machines, which should be made to vibrate continuously with amplitudes having variable value.
Said object is attained with the realization of a vibrating drum for soil tamping machines, which includes:
a cylindrical tubular skirt adapted to be arranged in abutment against the soil to be tamped;
one or more structural elements radially fastened inside said tubular skirt;
at least one central shaft in a through arrangement into said one or more structural elements, by which it is supported through rolling means;
flanging means adapted to make said drum integral with the frame of said tamping machine;
motorization means comprising at least a first hydraulic motor adapted to place said drum into rotation and vibration means adapted to make it vibrate during rotation,
wherein said vibration means comprises at least a second hydraulic motor coupled to an end of said central shaft, and at least one receptacle fastened to said central shaft, which delimits at least one chamber containing a liquid in which there is at least partly immersed at least one draught pipe connected through at least one duct to a hydraulic circuit external to said tubular skirt, said hydraulic circuit comprising pumping means adapted to change the amount of said liquid contained into said at least one chamber so as to change the vibration amplitude of said drum during rotation.
According to a preferred embodiment, inside the tubular skirt there is provided a radially arranged single chamber on a single side with respect to a plane passing through the longitudinal axis of said central shaft to which it is fastened.
The hydraulic circuit external to the tubular skirt is provided with a reversible pump, which through a feeding pipe makes the liquid circulate from the chamber inside the drum to an outer reservoir, and vice versa.
According to an embodiment variant, the reversible pump can be replaced by an irreversible pump associated to a dispenser.
According to a further alternative embodiment, inside the tubular skirt there are provided two chambers, arranged radially and at opposed sides with respect to the plane passing through the longitudinal axis of the central shaft to which they are fastened.
In all of the illustrated embodiments, the vibration means and the motorisation means comprise hydraulic motors.
There are also provided level indicators electrically connected to an electronic control gearcase, which automatically changes the liquid level inside the reservoirs according to the tamping degree of the soil.
Advantageously, the vibrating drum of the invention allows tamping different soils, with a better quality than that attainable using tamping machines provided with vibrating drums of the known type.